Image forming apparatus and image forming method

An image forming apparatus comprising:

• a rotatable image carrier configured to carry a toner image developed with toner on a surface of the image carrier surface;
• a rotatable transfer member configured to form a transfer nip by contacting the image carrier surface;
• a power supply configured to output a voltage to the recording material captured in the transfer nip to transfer the toner image formed on the image carrier surface;
• and
• a toner status determination unit configured to determine whether or not the toner is deteriorated and output toner information including that the toner is deteriorated when the toner status determination unit determines that the toner is deteriorated,
• wherein the voltage switches alternately between a voltage in a transfer direction to transfer the toner image from the image carrier and a voltage opposite to the voltage in the transfer direction when the toner image formed on the image carrier surface is transferred to the recording material,
• wherein a time average value (Vave) of the voltage has a polarity of the transfer direction to transfer the toner image from the image carrier to the recording material and is set to a value closer to a transfer voltage side from an intermediate value (Voff) between maximum and minimum values, and
• wherein a cycle of the voltage output from the power supply can be changed based on the toner information from the toner status determination unit.

A method of controlling an image forming apparatus having a power supply, the method comprising:

• developing a toner image on a surface of a rotatable image carrier with toner;
• forming a transfer nip by contacting a rotatable transfer member against the image carrier surface;
• supplying recording material to the transfer nip;
• outputting a voltage from the power supply to the recording material captured in the transfer nip to transfer the toner image formed on the image carrier surface to the recording material;
• and,
• changing a cycle of the voltage output from the power supply changed based on toner information indicating a state of deterioration of the toner,
• wherein the voltage alternates between a voltage in the transfer direction to transfer the toner image from the image carrier and a voltage opposite to the voltage in a transfer direction when the toner image formed on the image carrier surface is transferred to the recording material,
• wherein a time average value (Vave) of the voltage has a polarity of a transfer direction to transfer the toner image from the image carrier to the recording material and is set to a value closer to a transfer voltage side.